Cargo containers are the standard and most popular means for shipping materials by trucks, trains, and ships. Typically, several lifting points are located on the exterior of the containers to facilitate handling. Uniform lifting points are typically used so as to allow vehicular cranes or marine cranes to load or unload cargo containers onto flat bed trucks, railroad cars, or ocean-going vessels.
To meet the high demands of economical shipping, manufacturers are increasing the size of the cargo containers to create more shipping capacity per container. Specifically, these modern containers are being made wider than the pre-existing containers. These wider containers locate the top casting aperture, used for stacking and lifting the container, a greater distance from outboard wall of the container. The effect of increasing the distance of the aperture from the outboard wall and increasing the size and weight of the container is substantially higher stresses on the stacking frame when the container is stacked or lifted. One solution introduced to reduce these stresses is to move the aperture closer toward the outboard wall. However, these top castings fail to provide adequate space and strength to allow the containers to be lifted by a top picking apparatus. A solution is needed, therefore, that provides a top casting that positions the aperture closer to the outboard wall of a container to reduce stresses caused by stacking and lifting, and that at the same time provides adequate space and strength to permit top lifting operations.
Cargo container lifting devices currently in use are typically shaped to be inserted into top castings at the lifting points on the cargo containers and can be turned or twisted in the top casting to be secured therein. These lifting devices are usually T-shaped and are presented in one angular setting to be received by conventional top castings. Each top casting provides an upwardly opening aperture for receiving the lifting device. Typically, after the lifting device is inserted into the aperture of the top casting, the lifting device is then rotated through 90.degree. to a locking position. Once all lifting devices are locked to their respective top castings, the crane can begin lifting operations.
Standard cargo containers are manufactured in lengths of 10 feet, 20 feet, 30 feet, and 40 feet. Lifting points for these standard sized containers are generally located at or near the roof corners of the containers. The corner top castings have the benefit of two intersecting walls for support, namely the adjoining side wall and the end wall. In addition, the interconnection of a horizontal support between these top castings and a vertical post located at the intersection of the two walls aids in the structural integrity of the container.
Cargo containers also are manufactured in non-standard lengths in order to accommodate larger payloads while reducing associated shipping costs. These non-standard lengths are generally found in excess of 40 feet. Standard vehicular cranes and marine cranes must be capable of lifting such non-standard length containers. Therefore, lifting points are typically located or added at positions inboard from the ends of the containers. Lift fittings in the form of top castings are located at these lifting points. International standards require these top castings to be separated by 39 feet-4 inches center to center of the apertures.
Because the lifting points just described are located inboard from the ends of the container, a different support structure is required. These support frames are built into the structure of the containers. Although support frames are common for securing top castings, support frames do not provide as much support strength and rigidity as is available for the corner top castings on the standard length containers. Each support frame typically includes horizontal support members, vertical stacking posts, bottom castings and top castings. The upper horizontal support member extends between the side walls and is secured to the top castings. The lower horizontal support member extends between the side walls and is secured to the bottom castings. The vertical stacking posts support the side walls and couple respective top and bottom castings.
To facilitate secure and uniform stacking of cargo containers, bottom castings also include a downwardly opening aperture located from the outboard side a distance equal to the aperture of the top casting. International standards require 39 feet-4 inches between support frames and 89 inches between the apertures of each top casting set located a distance along the length of the cargo container. This standard spacing, along with the 40-foot standard spacing along the length of the container mentioned earlier, provides standard stacking points on cargo containers. These standards in turn allow for non-standard sized containers to be stacked with other containers. In order to lock stacked containers into place, IBC connectors are used between the top castings of a lower cargo container and the bottom castings of an upper cargo container. IBC connectors are container securement devices having upper and lower securing heads, similar to that of a top picking device. After the IBC connector head is located within the apertures of the top and bottom castings, the heads are rotated, locking the stacked cargo containers together. It should be noted that throughout the specification and claims herein, "connecting device" is defined as either a connecting device for an IBC connector or a connecting device for a top picker, or any other releasable engaging device used to connect the stacking post top casting via a top aperture to another conventional object or objects for stacking or lifting purposes.
Cargo containers have historically been manufactured to an exterior width that maintained the 89-inch separation between the apertures of the top castings to accommodate standard lifting devices. However, many more recent cargo containers have been manufactured with an increased width to increase cargo space. As a result, the top castings have become longer to maintain the coupling between the container side wall and the lift point of each top casting. In other words, the 89-inch distance between apertures of the top castings remains the same, but the distance between container side walls has increased, resulting in the need for longer top castings. Therefore, the distance between the aperture of each casting and the side wall of the container has increased.
Consequences of this increased distance are increased loads transferred to the stacking post and header during stacking and lifting operations. Because of the increased lateral spacing between these components, a longer moment arm subjects the stacking post to a larger torque loading. This type of loading has therefore introduced the necessity to provide additional strength to the support frames to withstand the loads imposed during stacking and lifting. Unfortunately, this increase in strength results in increased container weight, increased structural component size, decreased container capacity, and increased manufacturing costs.
One technique adopted to solve this problem, introduced by J. B. Hunt, is to position the aperture of each top casting closer to the outboard walls of the cargo container. For example, in a 1023/8 inch wide cargo container, the apertures are located 3.0" from the outboard walls. This creates a distance of 963/8 inches between corresponding top casting apertures, as opposed to the standard 89 inches of previous containers. This change in position decreases the length of the moment arm acting on the stacking post from the stacking forces transferred to the top casting at its aperture. The new aperture position has the effect of moving the applicable force closer to the axis of the stacking post, so as to provide the stacking post with better leverage against the induced stresses. With reduced stress, the overall weight of the frame and each top casting, the amount of intrusion into the cargo space, and the amount of equipment maintenance can be reduced. Although these top castings permit side lifting of the cargo container via a side aperture located on the outboard side of each top casting, they do not permit cargo container top lifting for various reasons. First, the cavity within this top casting does not allow adequate space for the top lifting device to fully penetrate the aperture (which is necessary to rotate the device head into the locked position). Second, even if the lifting device could fully penetrate the aperture, the internal walls of the top casting, specifically the outboard wall, would interfere with the rotation of the lifting device head. Third, it is questionable whether these top casting possess the strength characteristics necessary to allow lifting of the cargo container by the top apertures.
Due to the modified 963/8 inch spacing between apertures, it has become desirable to manufacture cargo containers that are compatible with both the 963/8 inch spacing as well as the standard 89 inch spacing for stacking purposes. To this effect, some J. B. Hunt containers have a top casting that has an outboard aperture located 3.0 inches from the outboard container wall as well as an inboard aperture located 611/16 inches from the outboard container wall. Therefore, a 1023/8 wide cargo container equipped with this top casting can be stacked with either a container utilizing the 963/8 inch spacing or the 89 inch spacing. However, like their counterpart top casting described earlier, these top castings do not permit top lifting operations and, instead, must be lifted by side lifting devices.
The design examples discussed above serve to illustrate the conflicting requirements of top castings. Top castings that locate the aperture near the outboard wall position the stacking forces closer to the stacking post for stability, but do not allow adequate cavity clearance for top picking devices. On the other hand, top castings that have an aperture located a substantial distance from the outboard wall provide adequate spacing for top lifting devices to operate, but require additional strength to maintain the support frames due to the increased moment forces acting on the stacking post imposed during stacking and lifting.
In light of the above design requirements and limitations, a need exists for a top casting which provides an aperture located near the outboard wall to reduce loads caused by stacking and lifting, provides adequate strength and cavity spacing to allow top picking of the cargo container, generates minimal interference with cargo container capacity, and provides capability for stacking with containers utilizing the 89 inch aperture spacing or the 963/8 inch aperture spacing. Each preferred embodiment of the present invention achieves one or more of these results.